In lamp heating and curing applications, a magnetron is used to provide microwave radiation to a lamp source, such as an electrodeless ultraviolet (UV) lamp used in the curing of adhesives, sealants or coatings in industrial applications. When the plasma of the lamp is sufficiently excited by the microwave radiation from the magnetron, the lamp illuminates to provide the necessary light wavelength and intensity for the particular heating or curing process.
Known magnetrons typically require one or more power supplies to be coupled to the magnetron for supplying the necessary anode DC current and filament voltage to the magnetron. The filament current of the magnet-on can be relatively high, such as 20 A or more depending on the operating specifications of the magnetron, so a filament transformer that supplies current to the filament is typically mounted at or near the magnetron to eliminate or at least reduce voltage drop in the interconnecting wires.
When the filament transformer is mounted remotely from the magnetron as may be required in certain applications, various approaches have been developed to compensate for the voltage drop in the interconnecting wires to provide the necessary filament voltage at the magnetron. In one approach, the output voltage of the filament transformer is increased at the terminals of the magnetron to compensate for the voltage drop in the interconnecting wires. The input voltage of the filament transformer is then trimmed by a series resistor or a tap associated with the filament transformer to provide the correct filament voltage for a given anode current or operating mode of the magnetron. Another approach is to phase control the voltage output of the filament transformer until the correct filament voltage is obtained.
However, in each of these known approaches, the filament transformer output voltage must be "calibrated" for each lamp heating or curing application to compensate for the voltage drop in the interconnecting wires. Moreover, these known approaches are not immune to variations in line input voltage to the filament transformer. That is, a proper setting or "calibration" of the filament transformer output voltage for one input line voltage will be adversely affected by a change in the input line voltage.
Thus, there is a need for a power supply that may be conveniently mounted remotely from a magnetron without requiring calibration for each lamp heating or curing application. There is also a need for a power supply in a lamp heating or curing system that is generally immune to voltage drops in the wires interconnecting the power supply to the magnetron. There is yet also a need for a lamp heating or curing system power supply that is generally immune to variations in the input line voltage to the power supply.